1. Field of the Invention
The present invention relates to a magnetic reproducing head in use with computers, video/audio/data tape recorders, and disc devices. Particularly, the invention relates to a magnetic reproducing head in which signal detecting portions of which the number is equal to "the number of recorded tracks to be subjected to concurrent reproduction process+1" are disposed on a single magnetoresistive effect element, whereby the head structure is simplified, and plural pieces of information are separately and concurrently reproduced from a plurality of recorded tracks.
More particularly, the invention relates to a multi-channel magnetic-resistance-effect (MRE) thin-film magnetic head for high track density reproduction, in which the magnetic head includes domain control layers bonded onto one of the larger surfaces of a single magnetoresistive effect element, and detecting electrodes being in close contact with the surfaces of the domain control layers, while being disposed in opposition to the magnetoresistive effect element with respect to the domain control layers. The domain control layers are vertically disposed on a region of a magnetic recording medium, the region being located between adjacent recorded tracks on the magnetic recording medium. The number of the domain control layers is equal to "the number of recorded tracks.+-.1". The width of each domain control layer is shorter than the width of a space between adjacent recorded tracks on the magnetic recording medium. With such a unique technical feature, plural pieces of information are concurrently reproduced from the recorded tracks in the form of potential differences each between adjacent detecting electrodes. The unique technical feature accrues to the following advantageous results. A reproduced crosstalk for a recorded track, which leaks from a recorded track or tracks adjacent to the recorded track (this or those adjacent tracks will be referred to simply as an "adjacent track"), is satisfactorily suppressed. Reproduced noises are little generated. A reproduced signal that is output from the resultant magnetic head is high in level.
2. Description of the Related Art
Attempt has been made to realize a multi-channel MRE thin-film magnetic head for high track density reproduction which is capable of concurrently reproducing information from a plurality of recorded tracks even where the track pitch (= the distance between two adjacent recorded tracks) is narrow. Such a magnetic head is disclosed as a magnetic reproducing head in Japanese Patent Unexamined Publication No. Hei 8-263812, and shown in FIG. 12.
The magnetic reproducing head disclosed in the publication is a multi-channel MRE thin-film magnetic head for high track density reproduction capable of concurrently reproducing information from a plurality of recorded tracks on a magnetic recording medium, such as a magnetic tape or a magnetic disc. The magnetic reproducing head includes a magnetoresistive effect element which is disposed crossing at least two recorded tracks on a magnetic recording medium, which the recorded tracks are to be subjected to concurrent reproducing process, and further detecting electrodes of which the number is equal to "the number of reproduced recorded tracks+1". The magnetoresistive effect element allows a flow of an internal current in a direction which depends on a sense current fed thereto, and has an easy axis of magnetization longitudinally oriented. The detecting electrodes are bonded on one of the large surfaces of the magnetoresistive effect element while vertically disposed between the recorded tracks. The multi-channel MRE thin-film magnetic head detects potential differences each between two adjacent detecting electrodes, and produces those in the form of reproduced signals.
The operation of the magnetic reproducing head thus constructed will described with reference to FIG. 12. A bias magnetic field is applied from a bias magnetic thin film 27 to a magnetoresistive effect element 5, while at the same time a sense current is fed to the same, whereby an initial state is set up in the magnetoresistive effect element. The bias magnetic field is directed upward or downward when viewed in the height directions of the magnetoresistive effect element (downward in FIG. 12). With the application of the bias magnetic field, an angle 9 developed between 1) an orientation of an internal magnetization of the magnetoresistive effect element 5, which is located in a region of a first channel (1st CH) defined between a first detecting electrode 8 and a second detecting electrode 9, and 2) an orientation of an internal current flowing through the magnetoresistive effect element 5, satisfies 10.degree..ltoreq..theta.80.degree. or 100.degree..ltoreq..theta.170.degree.. In the specification, .theta.=450.
The orientation of the internal magnetization of the magnetoresistive effect element 5 located in the 1 st CH region is rotated so that an angle .alpha. between its orientation and the orientation of the internal current satisfies a relation 0.degree..ltoreq..alpha..ltoreq.90.degree., in accordance with a magnitude of leaking flux by a signal (illustrated as a series of meshes and white stripes in FIG. 12) recorded in the first recorded track 2 on a magnetic recording medium 4. As a result, resistance of the magnetoresistive effect element 5 located in the 1st channel region varies (FIG. 12), and a reproduction voltage varies from B1 (low resistance state)--K1 (initial state)--A1 (high resistance state) in accordance with the recording signal of a first recorded track 2, to thereby form a first reproduced signal e1 (FIG. 13A).
Similarly, the angle, which is developed between an orientation of an internal magnetization of the magnetoresistive effect element 5, which is located in a region of a second channel (2nd CH) defined between the second detecting electrode 9 and a third detecting electrode 10, and an orientation of an internal current flowing through the magnetoresistive effect element 5, is .theta. in the initial state of the magnetic reproducing head.
The orientation of the internal magnetization of the magnetoresistive effect element 5 located in the 2nd CH region is rotated so that an angle .alpha. between its orientation and the orientation of the internal current satisfies a relation 0.degree..ltoreq..alpha..ltoreq.90.degree., in accordance with a magnitude of leaking flux by a signal (illustrated also as a series of meshes and white stripes) recorded in the second recorded track 3 on the magnetic recording medium 4. As a result, resistance of the magnetoresistive effect element 5 located in the 2nd channel region varies, and a reproduction voltage varies from A2 (high resistance state)--K2 (initial state)--B2 (low resistance state) in accordance with the recording signal of a second recorded track 3, to thereby form a second reproduced signal e2 (FIG. 13B).
In such a simple multi-channel MRE thin-film magnetic head, improper magnetic domains are generated in a ferromagnetic material (mainly Ni-Fe) used for the magnetoresistive effect element, and the Bloch or domain walls shift in the reproducing operation, thereby causing called Barkhausen noises to generate. To cope with this, a MRE thin-film magnetic head for one-track reproduction is disclosed in U.S. Pat. No. 4,103,315. In the magnetic head, as shown in FIG. 14, an external magnetic field of which the orientation is coincident with an orientation of an initial magnetization in the single magnetoresistive effect element on the easy axis of magnetization of the magnetoresistive effect element, is applied to a magnetoresistive effect element. As a result, a single magnetic domain is formed in the magnetoresistive effect element.
In the magnetic head, antiferromagnetic thin films 32, as shown in FIG. 14, are partially layered on both ends of a portion for sensing an external magnetic field (referred to as a magnetism sensing portion) of a magnetoresistive effect element 5. A magnetic field directed in an orientation of an initial magnetization in the single magnetoresistive effect element on the easy axis of magnetization of the magnetoresistive effect element 5, which is caused by exchange bond at the interface between the magnetoresistive effect element 5 and each antiferromagnetic thin film 32, is applied to the magnetism sensing portion.
A technique for improving the sensitivity of the magnetic head of the US patent is developed and disclosed in AP-A-3125311. A MRE thin film magnetic head of the Japanese publication uses a domain control for improving the sensitivity of the magnetic head, and a magnetoresistive effect element 5 is formed on only the magnetism sensing portion (FIG. 15). Hard magnetic thin films 34 are formed outside the magnetism sensing portion. A unidirectional magnetic field is applied to the magnetoresistive effect element 5. The unidirectional magnetic field is generated by magnetizing the hard magnetic thin films 34 so as to have an orientation of magnetization being coincident with the orientation of the initial magnetization in a single magnetoresistive effect element on the easy axis of magnetization of the magnetoresistive effect element 5.
In the magnetic reproducing head described in JA-A-8-263812, the following problem arises when the track pitch becomes short. A reproduction output signal detected in the region of the magnetoresistive effect element 5 vertically disposed on the guard band (FIG. 12) on the magnetic recording medium 4, which the guard band is located between two adjacent recorded tracks and has no information recorded therein, increases relative to a reproduced signal in the region of the magnetoresistive effect element 5 vertically disposed on each recorded track. In this state, a reproduction cross talk leaking from an adjacent track increases, and as a result, a signal to noise (S/N) ratio is deteriorated.
In the magnetic reproducing head of the above Japanese publication, it is expected that, by using a single magnetoresistive effect element 5, a single magnetic domain is set up in the magnetoresistive effect element 5 by increasing a crystal magnetic anisotropy of the magnetoresistive effect element 5 in a manner that the width (element width) of the magnetoresistive effect element 5 is set to be sufficiently larger than the height of the magnetoresistive effect element 5. However, such a setting of the width to height ratio is insufficient to form a single magnetic domain in the magnetoresistive effect element 5. Actually, improper magnetic domains are formed or irregular magnetization occurs in the magnetoresistive effect element 5. As a result, Barkhausen noise is generated, and the reproduced signals of the recorded tracks are not uniform.
Also, in the magnetic reproducing head described in U.S. Pat. No. 4,103,315, when the track width is reduced with increase of a recording density, a ratio of the width (element width) to the height (element height) of the magnetoresistive effect element 5 becomes small, and a crystal magnetic anisotropy of the magnetoresistive effect element 5 becomes small (for the element width and the element height, reference is made to FIG. 14). For this reason, an effective domain control of the magnetoresistive effect element 5 is impossible, resulting in generation of Barkhausen noise. In this respect, this magnetic head is not suitable for high track density reproduction.
Also, in the magnetic head disclosed in Japanese Patent Unexamined Publication No. 3-125311, when the track width is gradually reduced with increase of a recording density, a ratio of the width (element width) of the magnetoresistive effect element 5 to its height (element height) gradually decreases (for the element width and height, reference is made to FIG. 15), and a crystal magnetic anisotropy of the magnetoresistive effect element 5 becomes small. For this reason, a large hard magnetic thin film capable of generating a larger unidirectional magnetic field is required for effecting an efficient domain control of the magnetoresistive effect element 5. This makes it difficult to reduce the size of the magnetic head for the high track density reproduction purpose.